My mom told me to add one spoonful of sugar less than amount in recipe into cake batter.
The word ''less'' always confuses me. Is the way "less" is used in the sentence correct? If so, is it an adjective or adverb?
Dictionary result for less /lɛs/ determiner & pronoun determiner: less; pronoun: less 1. a smaller amount of; not as much. "the less time spent there, the better" synonyms: not so much, not so great, smaller, slighter, shorter, reduced; fewer "there was less noise now in the town" antonyms: more fewer in number. "a population of less than 200,000" synonyms: a smaller amount; More not so much as, not as much as, under, below; informalshy of "the fare is less than £1" antonyms: more adjectivearchaic adjective: less 1. of lower rank or importance. "James the Less" adverb adverb: less 1. to a smaller extent; not so much. "cut out less important material" synonyms: to a lesser degree, to a smaller extent, not so much, not as much; More rarely, barely, little, not much "we must consider the alternatives available so we can use the car less" antonyms: more far from; certainly not. "Mitch looked less than happy" preposition preposition: less 1. before subtracting (something); minus. "£900,000 less tax" synonyms: minus, subtracting, excepting, without, lacking "normally the buyer purchases at list price less 10 per cent" antonyms: plus
The sentence you have provided is correct. In this context less is used as a 'preposition'.
The meaning of the sentence -
You are supposed to subtract (minus) the amount of sugar specified by your mother (one spoonful) from the amount given in the recipe.
If the recipe said that you were supposed to add 5 spoonfuls of sugar, then your mother tells you to add 4 spoonfuls (5 spoonfuls - 1 spoonful)
I'm going to give you a simpler summary of what the other two answers say.
In theory, 'fewer' is used for countable objects (always in the plural) and 'less' for uncountable ones (which will always be singular).
There are fewer apples in the trees than last year. [note plural forms]
There is less water in the jug than earlier. [note singular forms]
Because 'spoonfuls' is a plural countable noun, 'fewer' would be preferred by strict grammarians, and in formal contexts.
In real life, however, many native English speakers are unaware of the rule and will very often use 'less' to mean 'fewer'. However, 'fewer' is never used with uncountable objects, so you can't reverse the process.
You can say (in informal contexts)
There are less apples in the trees than last year.
You cannot say:
There is fewer water in the jug than earlier.
The confusion may arise because the usual rule in more than, less/fewer than, is less for uncountable nouns, and fewer for countable nouns.
The sentence has a mix of countable and uncountable nouns:
one spoonful of sugar less than amount
one spoonful of sugar fewer than the number in the recipe 50g of sugar less than the amount in the recipe